In therapy planning for particle radiotherapy, an irradiation plan that defines control parameters for irradiating an examination object may be created in advance. The irradiation plan is used to plan the irradiation of an object in accordance with specific prescriptions (e.g., target volume or dose distribution).
Particle radiotherapy is a well-established method that may be used to irradiate tissue afflicted by tumor diseases. In particle radiotherapy, charged particles (e.g., protons, carbon ions, or other ions) are accelerated to high energies, shaped to make a particle beam, and conveyed via a high-energy transportation system to one or more irradiation rooms. The target volume of the treatment object is irradiated by the particle beam in an irradiation room. Tissue outside of the target volume may be irradiated as well.
If accelerators with an active energy variation are used in particle radiotherapy, particle beams with different energies are used for irradiating the target volume. As a result, isoenergy layers form that may lie in and outside of the target volume. In an isoenergy layer, the particle beam applies particles with the same energy, such that the particles of the particle beam to be positioned on the respective isoenergy layer have an energy that differs from the energy of the particles for other isoenergy layers. All particles for an isoenergy layer may be applied with the aid of one spill (e.g., by a single accelerator fill) since loading or generating a new spill takes a number of seconds. In total, the interruption time for generating a new spill takes up about half of the overall irradiation duration depending on the number of particles to be applied. To provide a patient-friendly irradiation of minimum duration, an accurate application of dose in the target volume, and an economical operation of the particle irradiation unit, the direct irradiation time and the overall irradiation duration may be minimized. The quality of the irradiation plan to be assessed by the treating medical practitioner may be considered.